What organic molecule is DNA?
• Nucleic Acid
Nucleic Acid
• An organic molecule containing hydrogen,
oxygen, nitrogen, carbon, and phosphorus
• Examples:
•
DNA
•
????
RNA
What differences do you see between DNA and RNA?
Differences between RNA and DNA
• 1. Sugar in RNA is ribose instead of
deoxyribose.
• 2. RNA is generally single stranded, not double
stranded.
• 3. RNA contains uracil instead of thymine
RNA
Is a disposable copy of a segment of DNA
FUNCTION:
Main function is protein synthesis.
Types of RNA
Messenger RNA (mRNA)
the RNA molecule that carries the copies of
instructions for assembling amino acids.
Ribosomal RNA (rRNA)
the RNA that combined with many other
proteins, make up the ribosomes that assemble
proteins
Transfer RNA (tRNA)
carries amino acids to the ribosomes and
matches them to the coded mRNA
What are the 3 differences between
DNA and RNA?
• RNA is a single strand, DNA double
• RNA has ribose sugar in it, DNA has
deoxyribose sugar
• RNA has the nitrogenous base uracil,
• DNA has thymine
How is RNA made?
• By process called transcription.
• Transcription – process in which segments of
DNA serve as templates to produce
complementary RNA molecules.
Where transcription occurs
• In prokaryotes it occurs in the cytoplasm
• In eukaryotes it occurs in the nucleus.
Transcription
1. The enzyme RNA polymerase attaches to
DNA strand
2. RNA polymerase separates the DNA strands
3. RNA polymerase uses one strand to assemble
nucleotides into RNA
Where does transcription start?
• The enzyme RNA polymerase binds to special
regions on the DNA called promoters.
• Promoters – specific base sequences on the
DNA that act as signals to show RNA
polymerase where to begin transcription
RNA editing
• Before the RNA can move on to make proteins
it must be “edited.”
• Pieces of the RNA are cut out. The pieces
that are cut out are called introns.
• The pieces remaining in the RNA are called
exons.
What is transcription?
• The process of making RNA from a strand of
DNA
• http://www.stolaf.edu/people/giannini/flasha
nimat/molgenetics/transcription.swf
How is RNA used to make proteins?
• The nitrogenous bases act as a code for
making proteins
Genetic code – The language consisting of 4 letters (A, C, G,
and U) that gives the instructions for building amino acids
The code is read three “letters” at a time, so each “word” is
three bases long
codon – the three letter word that
corresponds to a single amino acid
• There are 64 different 3 letter combinations of
the 4 bases A,T,C and G (so 64 codons)
• But there are only 20 amino acids. Why aren’t
there 64 amino acids?
Most amino acids can have more than one codon
that codes for them
ex. UUA, UUG, CUU, CUC, CUA and CUG all code
for the amino acid tryptophan
• There are also codons that that code for the
beginning and ending of protein synthesis.
“start” codons – where the reading of the mRNA
begins. (The amino acid methionine is a start
codon)
“stop” codon- where the reading ends.
*Amino acids bond together to make a polypeptide chain.
**Polypeptides- long chains of amino acids joined together.
• The amino acids in a polypeptide, and the
order in which they are joined, determine the
properties of the different proteins.
What do codons “code” for?
• Amino Acids
Translation
• After transcription the mRNA strand is ready
to start the process of protein synthesis.
• What part of the cell makes proteins?
Ribosomes
Ribosomes use the sequence of codons in
mRNA to assemble amino acids into
polypeptide chains.
Translation- The decoding of an mRNA
message into a protein
(Ribosomes translate the code)
Translation
Translation is carried out by ribosomes in the
cytoplasm.
Step 1: A ribosome attaches to mRNA
Translation
• Step 2: As each codon passes through
ribosome, tRNAs bring the proper amino acid
to the ribosome.
tRNA
• Each tRNA molecule carries just one kind of
amino acid.
• Each tRNA has 3 unpaired bases called an
anticodon.
• Each tRNA anticodon is complementary to one
mRNA codon
Translation
• Step 3:
•
The ribosomes attach the amino acids to
the growing chain.
Translation
• Step 4:
• The ribosomes helps form a peptide bond
between the first and second amino acid.
Translation
• Step 5:
• The ribosome then moves to the next codon
Translation
• Step 6:
• Polypeptide chain continues to grow until
ribosome reaches the stop codon
http://www.stolaf.edu/people/giannini/flashanimat/molgeneti
cs/translation.sw
f
How are proteins related to traits?
Many proteins are enzymes, which catalyze and
regulate chemical reactions.
Proteins regulate patterns of growth, patterns of
development in humans, and they build or
operate different components of a living cell.
The Central Dogma
• Information is transferred from DNA to RNA
protein